How to configure DNS nameservers on Ubuntu 18.04

On most Linux distributions you configure DNS nameservers in /etc/resolv.conf. However in recent versions of Ubuntu that changed with the introduction of Netplan.

Netplan is configured by editing YAML files located in /etc/netplan/. The precise name of this file will depend on your system configuration. I’m using an Ubuntu droplet on Digital Ocean, and the file is called 50-cloud-init.yaml.

Configure DNS nameservers

  1. Open the .yaml configuration file in /etc/netplan using your favourite text editor.

  2. In the ethernets section locate the network adapter you want to change the nameservers on (e.g. eth0)

  3. Add a nameservers section and list the addresses of the DNS nameservers you want to use, as shown in the example below:

    1
2
3
4
5
6
7
8
9

    network:
    version: 2
    ethernets:
        eth0:
            nameservers:
                addresses:
                - 1.1.1.1
                - 9.9.9.9
        # additional configuration omitted

  4. Save and close the Netplan configuration.

  5. To test your new configuration run:

    1

    sudo netplan try

    This will temporarily apply your new network configuration and automatically revert to the old one after 120 seconds. This lets you check your new configuration hasn’t broken everything. If you’re connected via SSH, and the connection hasn’t broken, then that’s a good sign. To accept the new configuration press Enter.

  6. To check that your DNS server configuration has changed run:

    1

    sudo systemd-resolve --status

    Scroll down until to find your network interface. You should see something similar to:

    1
2
3
4
5
6
7
8

    Link 2 (eth0)
        Current Scopes: DNS
         LLMNR setting: yes
MulticastDNS setting: no
        DNSSEC setting: no
    DNSSEC supported: no
            DNS Servers: 1.1.1.1
                         9.9.9.9

  7. A more thorough way to check you’re using DNS from the provider you’ve configured is to run a DNS query and get the IP address of the server that was used. An easy way to do this is to run the following DNS query:

    1

    nslookup -type=txt resolver.dnscrypt.info

    The txt record will contain the IP address of the resolver that was used. For me this returned:

    1

    resolver.dnscrypt.info  text = "Resolver IP: 162.158.110.213"

    A who.is lookup on this IP address reveals it belongs to Cloudflare, which suggests 1.1.1.1 is indeed being used to resolve DNS queries.

References